With reference to FIG. 12, a conventional heat-dissipation fan 200 comprises a base 210, an impeller 220 disposed at the base 210 and a lid 230, wherein the impeller 220 is covered with the lid 230. The impeller 220 comprises a hub 221 and a plurality of blades 222. When the impeller 220 is actuated to start rotation, the air is beaten by the rotating blades 222 to discharge laterally for achieving heat dissipation. However, an appropriate design of flow guidance is absent for the impeller 220. An air disturbance between the rotating blades 222 is occurred when the air is exhausted into the blades 222, which lowers air volume of heat dissipation and brings annoying noises.